There is a growing need in semiconductor manufacturing to deliver specialty gases to the point of use at high flow rates. Conventional compressed gas storage containers (herein after also referred to as “container”) such as, for example, vessels, cylinders and ton containers have liquefied gas under its own vapor pressure at ambient temperature. As the vapor is withdrawn from the container, the liquid evaporates at an equivalent rate to account for the decrease in pressure. This consumes energy from the remaining liquid in the container. In the absence of heat transfer to the container, the liquid temperature drops, leading to a corresponding drop in the vapor pressure. Further vapor withdrawal eventually subcools the liquid and the flow of vapor is reduced.
Along with liquid subcooling, rapid vapor withdrawal and uncontrolled heat transfer to the storage container also induces violent boiling at the container walls. This results in carryover of metastable liquid droplets into the vapor phase. In addition, the conventional sources of compressed gas storage deliver saturated vapor. A decrease in its temperature or a flow restriction in the process line leads to condensation. The presence of liquid droplets in the vapor stream is detrimental to most instruments and, therefore, needs to be minimized.
A solution is needed for three main reasons. First, chemical cost. In addition to the actual chemical cost savings there are savings that would be realized from getting the same amount of usable gas while handling fewer cylinders. Secondly, most liquified gasses are Green House gasses. Prime examples are Nitrous oxide, Carbon dioxide, hexafluoroethane and tetrafluoromethane. Said chemicals require additional weighing and documenting efforts in order to comply with existing Environmental Protection Agency Green House Gas requirements. There are possible future costs and impacts of EPA-mandatory reporting rule. Thirdly, the pressure instability can be an impact to process controls as regulators and mass flow controllers need to compensate.
In view of the foregoing, there is a need for a simplified method and system, which facilitates the withdrawal of gas from a compressed liquefied gas container by stabilizing the cylinder externally and passively to deliver high vapor flow rates from conventional sources, with minimal liquid carryover and without liquid subcooling.